The invention relates to an electronic device equipped with a touch panel and a method for determining coordinates.
As is well known, a touch panel is a combination of a display device, like a liquid crystal panel, with a touch pad (a position input device).
Some touch panels are of a capacitive type. The capacitive type touch panel enables performance of manipulation at a height within a predetermined range without contact of an indicator (a user's finger, a pen, and the like) with a panel screen (the proximal operation is hereunder called “hover manipulation”). FIG. 18 is a drawing showing a basic configuration of the capacitive type touch panel. In the drawing, a transmission electrode 101 and a receiving electrode 102 are disposed at a position distant from each other under a bottom surface of a plate-shaped dielectric 100. A drive pulse is applied from a drive buffer 103 to the transmission electrode 101. An electric field develops when the drive pulse is applied to the transmission electrode 101. When a finger is put in the electric field, the number of electric lines of force existing between the transmission electrode 101 and the receiving electrode 102 decreases. A change in the number of electric lines of force appears as a change in electric charges of the receiving electrode 102. An approach of the finger to the touch panel is detected by the change in the electric charges of the receiving electrode 102. An actual touch panel has the plurality of transmission electrode 101 and the plurality of receiving electrode 102 and two-dimensionally detects the finger.
FIGS. 19A to 19C are drawings showing a state of detection of the finger achieved when the finger is gradually brought closer to the touch panel. FIG. 19A shows a state in which the finger stays away from the electric field; FIG. 19B shows a state of detection of a hovering finger achieved when the finger has entered the electric field; and FIG. 19C shows a state of detection of a finger touch when the finger is fully in the electric field and remains in touch with the touch panel.
Hover manipulation awakes a response even when there is no touch with the touch panel. For this reason, there is a possibility that even user's unintended manipulation may have awaken a response. For instance, there is a response that will be awakened as a result of at least one finger approaching the touch panel when the housing is held with one hand or another response that will be awakened as a result of a base of the thumb approaching the touch panel when the touch panel is manipulated with one hand. The possibility of occurrence of such an erroneous operation becomes more noticeable when a casing trim of the housing becomes narrow or when the trim of the housing is rounded by making round edges between side surfaces and rear surface of the housing.
For instance, a fingertip touch determination device and a fingertip touch determination method that are described in connection with Patent Document JP-A-2012-164060 are mentioned as a technique for preventing the touch panel from responding to the user's unintended manipulation. Descriptions in Patent Document JP-A-2012-164060 mention that a determination can be made with high accuracy as to whether or not a fingertip remains in touch with a touch panel by evaluating kurtosis on the basis of values and positions of sensors of the touch panel where a peak appears in a data distribution of the sensor values.